Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$39.66	13.497%	$45.0129	$45.01	$45.00	$45.00
Purchase #2	$45.64	12.772%	$51.4691	$51.47	$51.45	$51.50
Purchase #3	$239.59	13.666%	$272.3324	$272.33	$272.35	$272.30
Purchase #4	$31.46	8.531%	$34.1439	$34.14	$34.15	$34.10
Purchase #5	$50.51	13.699%	$57.4294	$57.43	$57.45	$57.40
Purchase #6	$99.92	3.725%	$103.642	$103.64	$103.65	$103.60
Purchase #7	$99.89	3.199%	$103.0855	$103.09	$103.10	$103.10
7 purchase totals =	$606.67		$667.1152	$667.11	$667.15	$667.00